"RIR" with pea comb?

We got 25 straight run chicks from Sand Hill Preservation, that are about 12 weeks old. There were 6 RIR in the batch, but one of the (I think) pullets has a pea comb. Otherwise looks identical to the others. Ideas? Could it just be a mutation?

Hmmm, might be a rosecomb. I'm a bit of a newbie. Plus the comb is still pretty small as she (it) is only 12 weeks old. The RIR roos in the group have big red combs though. I'll need to go look at comb pictures and compare. Otherwise she looks just like the others in the group though.